This invention relates to a coating liquid composition which is for forming a hard and wear resistant coating film mainly on plastics articles and which is of the type containing a partial polycondensation product of an organosilanol and colloidal silica
Conventional plastics materials in wide use as moldable synthetic resins are generally low in surface hardness and are liable to be damaged by scratching. Therefore, often a protective coating film is formed on plastics articles. Particularly when importance is attached to good transparency of plastics materials as in the cases of polymethyl methacrylate resins and polycarbonate resins used as substitutes for inorganic glass, it is indispensable to protect the plastics surfaces with a hard and transparent coating film.
Several types of hard coating compositions have been developed for application to transparent and other plastics articles by using silicone resin, acrylic resin or melamine resin as the principal component, and at present silicone base hard coating compositions are prevailing mainly because of superiority in surface hardness and weatherability of the obtained coating films. In particular, hard coating compositions containing colloidal silica together with silicone are deemed best in respect of wear resistance of the obtained hard coating films.
As a proposal for improvements on hard coating compositions of the silicone and colloidal silica type, JP 52-39691 shows a coating liquid composition containing a polycondensation product of an organosilanol represented by the general formula RSi(OH).sub.3 (usually R is methyl group), colloidal silica, water and such an amount of acid that the pH of the liquid composition is in the range from 3.0 to 6.0. According to the description the acid controls the degree of condensation of the silanol and shelf life of the liquid composition, and the acid is selected preferably from water miscible carboxylic acids not having a cyclic structure, such as acetic acid, formic acid, propionic acid and maleic acid. However, this coating composition is not sufficient in storage stability and is not convenient for practical preparation because of bad reproducibility which is attributed to insufficient stability of an intermediate liquid composition, and hard coating films formed from this composition are not always satisfactory in some properties and particularly in wear resistance.